U.S. patent number 3,872,332 [Application Number 05/135,287] was granted by the patent office on 1975-03-18 for composite bond for acoustic transducers.
This patent grant is currently assigned to Honeywell Inc.. Invention is credited to Charles D. Butter.
United States Patent |
3,872,332 |
Butter |
March 18, 1975 |
COMPOSITE BOND FOR ACOUSTIC TRANSDUCERS
Abstract
A piezoelectric transducer is bonded to an acoustic medium by a
composite bond formed by a polymerizable plastic material and a
sheet-like grid. Proper selection of the material and percentage of
open space of the grid allows the acoustic impedance of the
composite bond to be adjusted to a desired value.
Inventors: |
Butter; Charles D. (Eden
Prairie, MN) |
Assignee: |
Honeywell Inc. (Minneapolis,
MN)
|
Family
ID: |
22467402 |
Appl.
No.: |
05/135,287 |
Filed: |
April 19, 1971 |
Current U.S.
Class: |
310/334; 310/365;
367/152; 310/363 |
Current CPC
Class: |
H01L
41/047 (20130101); G10K 11/02 (20130101) |
Current International
Class: |
G10K
11/02 (20060101); H01L 41/00 (20060101); H01L
41/047 (20060101); G10K 11/00 (20060101); H01v
007/00 () |
Field of
Search: |
;310/8.2,8.3,9.6,9.7,8
;340/8MM ;333/3R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Budd; Mark O.
Attorney, Agent or Firm: Fairbairn; David R.
Claims
The embodiments of the invention in which an exclusive property or
right is
1. An acoustic device comprising:
a piezoelectric transducer having a first and a second surface and
a first acoustic impedance,
an acoustic medium having a third surface and a second acoustic
impedance different from the first acoustic impedance,
first electrode means attached to the first surface, a sheet-like
electrically conductive metal mesh positioned between the second
and third surfaces and forming a second electrode means, the
electrically conductive metal mesh having a plurality of openings
therein, and,
a polymerizable plastic material filling the openings of the
electrically conductive metal mesh and adhering to the second and
third surfaces, the electrically conductive metal mesh and the
polymerizable plastic material forming a composite bond having a
third acoustic impedance essentially equal to the square root of
the first and second acoustic impedances, the third acoustic
impedance being determined by the impedance of the electrically
conductive metal mesh, the impedance of the polymerizable plastic
material, and the percentage of open space in the electrically
2. The invention that is described in claim 1 wherein the
polymerizable plastic material is epoxy.
Description
BACKGROUND OF THE INVENTION
This invention relates to an acoustic device having an improved
bond between a piezoelectric transducer and an acoustic medium.
One type of acoustic device in which the present invention can be
used to a particular advantage is an acousto-optic light beam
deflector. In this device light waves are diffracted by acoustic
waves, resulting in the deflection of the light waves to a
particular angle or angles depending upon the frequency of the
acoustic waves.
In the prior art, problems have arisen in bonding a piezoelectric
transducer to an acoustic medium since typically the acoustic
impedances of the piezolectric transducer and the acoustic medium
are different. Therefore, the ideal acoustic impedance of the
bonding material is equal to the square root of the product of the
impedances of the acoustic medium and the piezoelectric transducer,
so that impedance matching is achieved. However, it has been very
difficult to select a bonding material which has this ideal
acoustic impedance.
SUMMARY OF THE INVENTION
The present invention provides an improved bond for which the
proper acoustic impedance can be achieved by a simplified
procedure, thereby reducing the cost of fabrication.
A sheet-like grid is positioned between a surface of the
piezoelectric transducer and a surface of the acoustic medium
desired to be bonded. The sheet-like grid has a plurality of
openings therein. A polymerizable plastic material fills the
openings of the sheet-like grid and adheres to the surfaces of the
transducer and the acoustic medium. The sheet-like grid and the
polymerizable plastic material thereby form a composite bond.
The acoustic impedance of the composite bond is adjusted to a
desired value by proper selection of the material forming the grid
and the percentage of open space in the grid.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a piezoelectric transducer and an acoustic medium
prior to formation of the improved bond of the present
invention.
FIG. 2 shows an acoustic device having a piezoelectric transducer
bonded to an acoustic medium by the improved bond of the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, an acoustic device is shown prior to formation
of the improved bond of the present invention. Piezoelectric
transducer 10 having a first surface 12 and a second surface 14 is
positioned opposite acoustic medium 20. Located on a third surface
22 of acoustic medium 20 is a polymerizable plastic material 26.
Positioned between second surface 14 and third surface 22 is a
sheet-like grid 30. Extending through the sheet-like grid are a
plurality of openings.
Upon bonding, polymerizable plastic material 26 fills the
interstices or openings of sheet-like grid 30 and adheres to second
surface 14 and third surface 22. In this manner, the sheet-like
grid 30 and polymerizable plastic material 26 form a composite
bond.
The acoustic impedance of polymerizable plastic material 26 differs
from that of sheet-like grid 30 and therefore by selecting the
appropriate percentage of open space of sheet-like grid 30 it is
possible to achieve a composite bond having a desired acoustic
impedance. Since sheet-like grid 30 ordinarily has the larger
acoustic impedance, a reduction in the percentage of open space
increases the acoustic impedance of the composite bond. Further
adjustment of the acoustic impedance of the composite bond is
achieved by utilizing different material for the sheet-like
grid.
FIG. 2 shows a completed acoustic device having a composite bond.
In this embodiment sheet-like grid 30 comprises a metal mesh. A
first electrode 40 is attached to first surface 12 of piezoelectric
transducer 10. The metal mesh comprising sheet-like grid 30 forms a
second electrode adjacent second surface 14. Electrical leads 50
and 52 are attached to first electrode 40 and sheet-like grid 30,
respectively, so that an electrical signal can be applied to
piezoelectric transducer 10.
In one successful embodiment of the present invention a 35.degree.
Y-cut Lithium Niobate crystal having an acoustic impedance of
approximately 34.8 .times. 10.sup. 6 Kg/m.sup.2 sec is used as the
piezoelectric transducer. The crystal is approximately 10
millimeters long, 1.5 millimeters wide and 80 microns thick. The
acoustic medium is a body of fused quartz having an acoustic
impedance of 13.1 .times. 10.sup.6 Kg/m.sup.2 sec. A 0.3 mil thick
copper mesh having 750 lines per inch and 55% open area is
positioned on one surface of the acoustic medium. An epoxy
material, Epon 815 manufactured by Shell Chemical Company, is
placed on top of the copper mesh so that the interstices or open
spaces in the mesh are filled with the epoxy. The transducer is
then placed on top of the metal mesh and epoxy so that it becomes
fixed to the fused quartz acoustic medium. The composite bond thus
formed has an acoustic impedance of approximately 21.3 .times.
10.sup.6 Kg/m.sup.2 sec, which is very close to the ideal value for
acoustic impedance matching.
In operation the bonded transducer is utilized in an acousto-optic
light beam deflector. The fused quartz acoustic medium is placed in
a housing so as to contact water. The acoustic signal produced by
the piezoelectric transducer is directed through the fused quartz
and into the water. A light beam directed through the water is
deflected by an angle dependent upon the frequency of the acoustic
signal.
While this invention has been disclosed with particular reference
to the preferred embodiments, it will be understood by those
skilled in the art that changes in form and details may be made
without departing from the spirit and the scope of the invention.
For example, the sheet-like grid need not be electrically
conductive. In that case, an evaporated conducting film on the
transducer forms the second electrode.
* * * * *